What is it?
A type of cardiovascular training that has become popular recently is commonly referred to as fasted cardio training. The term “fasted cardio” refers to the practice of performing low intensity cardiovascular exercise immediately after waking up, before eating breakfast.
Why does it sound like a good idea?
Those who choose to conduct fasted cardio typically have two hopes: First that your body will turn to its adipose tissue for stored energy in the absence of fresh glucose in your bloodstream (i.e. you will burn more fat). Second, that exercise done in this fasted state will also target the “stubborn fat stores” on your body, typically hips and thighs for women, stomach for men.
Does the idea hold water?
Regarding your ability to access stored fat on an empty stomach, fasted cardio comes up short. Unfortunately you cannot effectively control where your body is pulling stored fuel from. While some of the energy you will utilize to fuel your fasted cardio session will indeed come from adipose tissue, some energy will also emerge from glycogen stores in your muscles and liver, and still more will come from protein stored in your muscle tissue. Additionally, fat burns in the flame of carbohydrate, and without fresh glucose in your system your metabolism will be operating at a reduced capacity, lessening your ability to burn fat in general, as well as your general capacity to power through your workout.
As for targeting those stubborn areas on your body, that should sound too good to be true, and it is. Body fat is gained and lost at an equal percentage rate all over your body. While you store fat in certain areas more than others, if you lose 1% body fat you lose 1% of the fat stored in your hands and you lose 1% of the fat stored in your hips. That is the way your body works, irrespective of the frequency, intensity, duration, and mode of exercise you choose to participate in.
In the end, fasted cardio is a bad idea. It is ineffective, metabolically inefficient, and has the potential to be dangerous, as your risk of slipping up during exercise increases dramatically when you have not eaten. Always eat your breakfast, and if you are interested in improving your body composition hit the weights, not the treadmill.